Brazil is experiencing a huge dengue outbreak, the sometimes fatal disease transmitted by mosquitoes, and public health experts say it is a harbinger of an upcoming increase in cases in the Americas, including Puerto Rico.
Brazil's Ministry of Health warns that it expects more than 4.2 million cases this year, surpassing the 4.1 million cases recorded by the Pan American Health Organization in the 42 countries of the region last year.
El Niño and climate change
Brazil was expected to have a bad year for dengue (the number of cases of the virus generally rises and falls in a cycle of about four years), but experts say thate a number of factors, including El Niño and climate changehave significantly amplified the problem this year.
“The record heat in the country and the above-average rainfall since last year, even before the summer, have increased the number of mosquito breeding sites in Brazil, even in regions that had few cases of the disease,” said the minister. of Health of Brazil, Nísia Trindade. she said.
A health agent inspects jars and containers to make sure they do not contain water. Photo: Reuters
The number of dengue cases it has already been shot in Argentina, Uruguay and Paraguay in recent months, during the southern hemisphere summer, and the virus will rise across the continent with the seasons.
“When we see waves in a country, generally we will see waves in other countries; That's how interconnected we are,” said Dr. Albert Ko, an expert on dengue in Brazil and professor of public health at Yale University.
Dengue: an urgent global health problem
The World Health Organization has warned that dengue is rapidly becoming an urgent global health issuewith a record number of cases last year and outbreaks in places, like France, that have historically never reported the disease.
In the United States, Dr. Gabriela Paz-Bailey, chief of the dengue section of the division of vector-borne diseases at the Centers for Disease Control and Prevention, said that expected high dengue infection rates in Puerto Rico this year and that There would also be more cases in the continental United States, especially in Florida, as well as in Texas, Arizona and southern California.
Dengue is transmitted by Aedes aegypti, a species of mosquito that is establishing itself in new regions, including warmer, wetter parts of the United States, where it had never been seen until recent years.
A mosquito larva taken during a check in an old shed in Rio de Janeiro. Photo: Reuters
Cases in the United States are still expected to be relatively few this year (hundreds, not millions) due to the prevalence of air conditioning and window screens. But Paz-Bailey warned: “When you look at the trends in the number of cases in the Americas, it is scary. “It has been increasing steadily.”
Florida reported its highest number of locally acquired cases last year, 168and California reported its first such cases.
Three quarters of people infected with dengue they do not have any symptoms and, among those who do have it, most cases will resemble only a mild flu. But some dengue infections They are serious and cause headaches, vomiting, high fever, and joint pain. which gives the disease its nickname “bone-breaking fever.” A severe case of dengue can leave a person weakened for weeks.
And about 5% of people who get sick will progress to what is called severe dengue, which causes plasma, the protein-rich liquid component of blood, to leak from blood vessels. Some patients may go into shock and cause organ failure.
Severe dengue has a mortality rate of 2% to 5% in people whose symptoms are treated with blood transfusions and intravenous fluids. However, if left untreated, the mortality rate is 15%.
In Brazil, state governments They are creating emergency centers to test people for dengue and treat them. The city of Rio de Janeiro declared a public health emergency over dengue on Monday, days before the start of the annual Carnival celebration, which draws tens of thousands of people to outdoor parties during the day and night.
Trindade said a large number of cases are being reported in Brazil's southernmost states, which tend to be much colder than Rio and the central and northern states. People in those areas will have little immunity to the disease due to previous exposure.
Dengue occurs in four serotypes, which are like cousin viruses. Previous infection with one offers only short-term protection against infection with another, and a person who has had one dengue serotype in the past is at increased risk of developing severe dengue from infection with another serotype.
A drone fumigates parts of Brasilia. Photo: AP
“At this moment they are circulating in Brazil serotypes that have not circulated in 20 years“said Dr. Ernesto Marques, associate professor of infectious diseases and microbiology at the University of Pittsburgh.
The Japanese Qdenga vaccine
Brazil has started an emergency campaign to immunize children in areas with the highest rates or risk of dengue transmission, using a two-dose vaccine called Qdenga which is manufactured by Takeda Pharmaceutical Co. of Japan.
Brazil purchased 5.2 million doses for delivery this year, plus 9 million more for delivery in 2025, and the company donated an additional 1.3 million, effectively blocking most of Qdenga's supply globally. A company spokesperson said Takeda is working on a plan to increase supply, focusing on delivery to countries with high prevalence.
A new vaccine with a single dose
But still, that's enough to cover less than 10% of the Brazilian population in two years. The only good news about dengue in Brazil at the moment is the publication of the results of clinical trials of a new vaccine tested by the Butantan Institute public health research center in São Paulo.
That vaccine requires only one injectionand the trial found that protected 80% of those vaccinated against the development of dengue virus disease. The research center will ask the Brazilian government for approval of the vaccine and has facilities to produce it, with the goal of beginning to administer injections in 2025.
Few ways to stop the current outbreak
For this outbreak, it is too late for vaccination to help much and public health authorities have few other ways to slow it down.
“The insecticide resistance actually limits what can be done in terms of controlling the mosquito population, and insecticide resistance is widespread,” Paz-Bailey said. “What can be done is ensuring that people have access to clinical management and that doctors know what to do.
Medical centers in Brazil are setting up extra beds for people with severe dengue, hoping to avoid the kind of overloading of health systems that occurred during the COVID-19 pandemic and prevent dengue deaths.
“The old paradigm that dengue affects children more is not the case in Brazil; you have to think about the elderly, who are very vulnerable,” Ko said. It will be important for both doctors and the public to understand the message of carrying out dengue testing at the first sign of symptoms in both children and older people, he said.
“Any educated assumption was that this would be a bad year,” Marques said, “but now we know how bad it will be. It's going to be very, very bad”.
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